Exposure of humans to radiation can cause serious harm, even death. Exposure can be accidental, resulting, for example, from a radiation leak at a nuclear power plant. Exposure also can be intentional, resulting, for example, from an act of terror. The most common circumstance of radiation exposure results from medical interventions, such as for the treatment of cancer. Radiation in this context can be local or systemic. When applied locally, radiation can nonetheless cause unwanted injury to healthy tissue in the pathway of the radiation. When applied systemically (i.e., total body irradiation), low doses can lead to bone marrow damage and gastrointestinal tract toxicity. High doses of total body irradiation can lead to permanent bone marrow damage, gut and lung toxicity, and sometimes death. There is a need for effective treatments which protect healthy tissues and mitigate the acute and chronic effects of exposure to ionizing radiation.